pgsql: Fix pg_amcheck --skip option parameter handling

Fix pg_amcheck --skip option parameter handling

The skip options set for all-visible and all-frozen were incorrect
as they used space rather than hyphen, causing a syntax error when
invoked. Also, the option for not skipping any pages at all, none,
was documented but not implemented.

Backpatch through 14 where pg_amcheck was introduced.

Bug: #17149
Reported-by: Chen Jiaoqian <chenjq(dot)jy(at)fujitsu(dot)com>
Reviewed-by: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
Discussion: https://postgr.es/m/17149-5918ea748da36b15@postgresql.org
Backpatch-through: 14

Branch
------
REL_14_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/5310c61ecc14f23d28429f055c968a97d5e8b39c

Modified Files
--------------
src/bin/pg_amcheck/pg_amcheck.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)